This invention relates generally to bus communications between a microprocessor controller, or central control unit (CCU), and function control units that have identical digital addresses. More specifically, the invention is concerned with operating a television receiver (TV) having a digital chassis including a number of digitized function control units and a picture-in-picture module including digitized function control units where one or more pairs of the individual function control units have the same digital addresses.
The prior art includes so-called digital TV receivers in which digital signals and functions controls are used rather than conventional analog signals and control devices. The many advantages associated with a digital TV receiver include uniformity of product, precise control of signal parameters and operating conditions, elimination of mechanical switches and a greatly enhanced potential for reliability. Television receiver Model No. SD2035H from Zenith Electronics Corporation embodies such a digital chassis. In particular, it includes a high speed communications bus for interconnecting a CCU with various TV function modules for processing a TV signal. The modules include a deflection processing unit, a video processing unit, an automatic phase control, a video codec unit, an audio analog to digital converter, and an audio processing unit. The system and its various integrated circuit chips is generally described in DIGIT 2,000 VLSI Digital TV System developed by ITT Intermetall and published in edition 1984/85 order No. 6250-11-2E. The interconnection and general operations of the various function control units in the digital TV chassis and the so-called IM (Intermetall) bus are disclosed in U.S. Pat. No. 4,649,428, issued 3/10/87 and assigned to Zenith Electronics Corporation and which is hereby incorporated by reference.
A rapidly growing feature in TV receivers is the so-called picture-in-picture (PIP) which enables a viewer to selectively watch a different television presentation as an inset on the main television presentation. The present invention is particularly concerned with the PIP system used in a digital TV chassis such as that described in the above-mentioned '428 patent.
In the PIP system, many of the function control units are identical to those in the digital chassis. In the interest of economy, it is desirable to utilize identical (or substantially identical) integrated circuit chips to implement the PIP function. A formidable difficulty arises, however, where the IC chips in the PIP module have the same digital addresses as their counterparts in the digital chassis, since the IM bus communications system is incapable of differentiating between function control units having the same digital addresses.
Accordingly, it would be highly desirable to have a means and method of operating such an IM bus system with a plurality of function control units that have the same digital addresses.